JOURNAL OF CHEMICAL EDUCATION
AN INEXPENSIVE THERMOSTAT WILLIAM P. LINRE New York University, New York, New York
THIS simple and surprisingly efficient thermostat can
be assembled in a matter of minutes. The materials are available in every laboratory, and its flexibility and accuracy rival many expensive installations. Because regulators, relays, and heaters are not needed, the setup is especially appropriate where low cost is important. In this laboratory it has been used for solubility determinations in which many different temperatures were required for short periods of time. A one-liter, thre+necked flask is fitted as shown in the diagram. The sample is placed in the test tube. Any desired temperature between about 60" and 200° can then be maintained by an appropriate selection of the boiling liquid. Mixtures can be prepared which will boil at any chosen temperature. They can be made from a wide variety of substances, and may be organic or inorganic solutions. When a mixture of liquids is used, it has been found convenient to start with about 100 ml. of the higherboiling liquid in the flask. The boiling is begun and the second liquid is added in small portions until the boiling point of the mixture has fallen to the desired temperature. The additions are made through the open end of the reflux condenser, and the boiling is continuous during the adjustment. The inner walls of the condenser may be flushed down by temporarily shutting off the cooling water. During a typical rnn using an acetic acid-water mixture, the observed temperature was 110.0' for six hours, with a maximum variation of + 0.1". For greater accuracy, the thermometer can be calibrated under the experimental conditions by using a substance of known boiling point.
